Analysis of the causes of a 5″ drill rod leakage in a well

To analyze the causes of 5″ drill pipe leakage in a well, the materials of drill pipe samples were analyzed by chemical composition analysis, mechanical properties test, metallographic analysis, grain size evaluation and non-metallic inclusion evaluation, the cracks around the drill hole were analyzed by metallographic analysis, fracture macro analysis and scanning electron microscopic analysis, the corrosion products at the bottom of the corrosion pit were analyzed by EDS, the drill pipe penetration mechanism was simulated and analyzed. The finite element simulation analysis was carried out. The chemical composition and mechanical properties of the drill pipe meet the requirements of API Spec 5DP—2009 standard. The impact toughness of the drill pipe is higher (the impact energy of the two drill pipes is 83 J and 87 J respectively), which is more than twice the technical standard; the structure of the drill pipe sample is tempered sorbite, which is the normal tempered structure morphology; the grain size of the drill pipe sample is 9 grades, and the non-metallic inclusion. The highest grade is 1.0, which meets the requirements of product technical standards; there are a lot of corrosion pits on the outer wall of the drill pipe, and there are corrosion products of oxygen element at the bottom of the corrosion pit, that is, oxygen corrosion; the extension crack of the piercing hole and its surrounding cracks are relatively straight, and there are fatigue striations at the tip of the crack, which proves that the piercing propagation is carried out in the form of fatigue cracks. The penetration of the two drill pipes belongs to early corrosion fatigue damage. The causes are as follows: (1) Dissolved O in drilling fluid corrodes the outer wall of the drill pipe seriously and forms deep corrosion pits; (2) Small cracks are sprouted at the bottom of the corrosion pit when passing through the severe dogleg section, and then fatigue cracks propagate under rotating bending force until they penetrate into the wall thickness of the drill pipe; (3) In order to prevent the early failure of defective drill pipes, rigorous detection of drill pipes passing through the well is carried out. © 2020, Chongqing Wujiu Periodicals Press. All rights reserved.